A screen for all places

JENA/DRESDEN, Germany – Cell phones and PDAs have become more than just communication devices – they also are multimedia entertainment tools. It no longer seems unusual to view photos and video clips through them, or even to watch entire television shows and movies. However, their small screen size makes sharing the viewing experience a difficult task – either everyone crowds around the device, or it is passed around while the clip or image is displayed repeatedly. A simple, portable way to share the experience with friends and family in a larger format surely would be popular.

A miniature projector would enable users to display images from their cell phones on a larger surface. Courtesy of Fraunhofer-Gesellschaft.
A team of researchers at Fraunhofer Institute for Applied Optics and Precision Engineering, in collaboration with other members of the European Union-funded HYPOLED (High-Performance OLED-Microdisplays for Mobile Multimedia HMD and Projection Applications) project, has developed a miniature projector designed for integration into cell phones and PDAs. The prototype is 2.5 cm long and 1.8 cm in diameter, does not require an additional light source and uses only a small amount of energy to operate. It has a working distance of between 300 and 500 mm, and the projection system magnifies the image by 12× to 15×.

The device employs an organic LED (OLED) display that was developed at Fraunhofer Institute for Photonic Microsystems in Dresden to produce the images. It projects monochrome images with a microdisplay brightness of 10,000 cd/sq m, and color images at about half that brightness.

This OLED microdisplay could mean the end of watching videos on tiny cell phone screens. Courtesy of Uwe Vogel.
Stefan Riehemann, leader of the research group, said this level of brightness can be put into perspective by realizing that a typical computer monitor produces between 150 and 300 cd/sq m.

The image produced by the OLED display is projected through a series of five lenses onto any chosen flat surface. The prototype uses glass lenses, but investigators are trying to create plastic lenses that could be easily mass-produced to perform the same function. This change would make commercialization of the product more feasible.

But there is still work to be done in refining the concept before releasing the product onto the market. Uwe Vogel of the Fraunhofer Institute for Photonic Micro-systems and coordinator of HYPOLED, said, “Very high brightness OLED micro-display[s] can just be reached by monochrome emitters, so full color is more demanding.”

A transmissive, reflective or emissive high-resolution display that typically measures 1 cm diagonally, and whose use requires magnifying optics to project a highly magnified image on a surface for the image to be observed by the viewer.